This invention discloses a process for treating polyester fabrics so as to improve their moisture wicking, soil-release, soil-redeposition, and anti-static characteristics.
Although polyester fabrics have been used successfully in the manufacture of clothing, for a long time, such fabrics have several disadvantages. Polyester fibers do not have the excellent moisture wicking properties of cotton yarns. That is, moisture deposited on the polyester fiber tends to remain where it is, and is not easily carried away along the fiber. Fabrics made of polyester feel uncomfortable when worn near the skin because body moisture cannot easily spread and evaporate. Thus, polyester fabric has been used to make fine outerwear, but has been considered unacceptable in the intimate apparel or active sportswear market.
The hydrophobic nature of polyester fiber, which results in its inferior wicking characteristics, also contributes to its poor soil-resistance properties. Since polyester fabrics are both hydrophobic and oleophilic, they tend to pick up oil-based stains which are not easily removed by rinsing. As polyester fabrics also tend to pick up soil during laundering, such fabrics often become increasingly gray after continued washings.
Another disadvantage of polyester is its tendency to cling because of a build-up of electrostatic charges. The tendency toward static cling is another factor that has made polyester fabric unsuitable for the intimate apparel market.
There have been many attempts to solve the above-described problems of polyester fabrics, some of which have been partially successful. One method is to use a finishing agent on the fabric which would impart properties of soil-release, increased water absorbency, and improved anti-static properties. The finishing agents which have been used are essentially copolymers having both hydrophilic and oleophilic groups. The oleophilic groups can be introduced into the polyester fiber such that the hydrophilic groups remain on the surface, thereby imparting the desired properties. The finishing agents have been applied to polyester by padding and drying and heat setting. Finishing agents have also been applied during the dyeing operation, by exhausting the product onto the fiber.
Finishing agents of the type described have been marketed under the name of Zelcon 4730 (by the E. I. duPont Company) and Milease T (by Imperial Chemical Industries). Details of such finishing agents are given in U.S. Pat. Nos. 3,416,952, and 3,557,039.
In particular, as described in U.S. Pat. No. 3,557,039, such a finishing agent can comprise an aqueous dispersion of 10-50% by weight ethylene terephthalate units, together with 50-90% by weight polyoxyethylene terephthalate units, wherein the average molecular weight of the polyoxyethylene units is 1000 to 4000, wherein the molar ratio of ethylene terephthalate to polyoxyethylene terephthalate is in the range of 2:1 to 6:1, the viscosity ratio of the copolymer being between 1.10 and 1.50, and the melting point being above 100.degree. C., as measured by the temperature of disappearance of birefringence.
One disadvantage of copolymers such as Milease-T is that the anti-static property does not remain as the fabric is laundered many times. Of course, a fabric is not useful if its necessary characteristics are not permanent.
Another method of improving the properties of polyester fabrics has been to treat the polyester with sodium hydroxide. A caustic solution would be used to attack the polyester polymer chain chemically, preferably in the presence of a suitable catalyst such as a quaternary ammonium compound. The catalyst, after being exhausted onto the fiber, would provide an affinity for the caustic to attach to the fiber. This treatment results in the formation of carboxyl groups on the surface of the polyester polymer. The carboxyl groups tend to make the polyester fabric more hydrophilic, thereby improving its moisture-wicking, anti-static and other properties. However, the improvement which results from this treatment is not especially great, and the process is somewhat difficult to control, because it is necessary to attack the fiber uniformly, and to stop the process before the fiber is unduly weakened. Also, the caustic treatment gives very little improvement in anti-static properties at low humidities.